docs: Filled in some missing `\param` and `\returns` sections.

src/physfs.h

@@ -1001,6 +1001,13 @@ extern PHYSFS_DECL int PHYSFS_CALL PHYSFS_setWriteDir(const char *newDir);
  * \deprecated As of PhysicsFS 2.0, use PHYSFS_mount() instead. This function
  *             just wraps it anyhow.
  *
+ * \param newDir directory or archive to add to the path, in
+ *               platform-dependent notation.
+ * \param appendToPath nonzero to append to search path, zero to prepend.
+ * \returns nonzero if added to path, zero on failure (bogus archive, dir
+ *          missing, etc). Use PHYSFS_getLastErrorCode() to obtain the
+ *          specific error.
+ *
  * \threadsafety It is safe to call this function from any thread.
  *
  * \since This function is available since PhysicsFS 1.0.0.
@@ -1030,6 +1037,10 @@ extern PHYSFS_DEPRECATED PHYSFS_DECL int PHYSFS_CALL PHYSFS_addToSearchPath(cons
  *             the preferred way to accomplish this function's work is now
  *             called "unmounting."
  *
+ * \param oldDir dir/archive to remove.
+ * \returns nonzero on success, zero on failure. Use PHYSFS_getLastErrorCode()
+ *          to obtain the specific error.
+ *
  * \threadsafety It is safe to call this function from any thread.
  *
  * \since This function is available since PhysicsFS 1.0.0.
@@ -2793,6 +2804,10 @@ extern PHYSFS_DECL void PHYSFS_CALL PHYSFS_getSearchPathCallback(PHYSFS_StringCa
  *             your callback has no way to direct the process, and your
  *             calling app has no way to know.
  *
+ * \param dir Directory, in platform-independent notation, to enumerate.
+ * \param c Callback function to notify about search path elements.
+ * \param d Application-defined data passed to callback. Can be NULL.
+ *
  * \threadsafety It is safe to call this function from any thread, but this
  *               function will hold a lock that prevents many other PhysicsFS
  *               functions from running until your callback returns and this